<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>按钮</button>
    <script>
        var btn = document.querySelector('button');
        btn.onclick = function() {
            this.disabled = true; //这个this指向的是btn这个按钮
            setTimeout(function() {
                this.disabled = false; //定时器里面的this指向的是window
            }.bind(this), 3000) //这里的this指向的是btn这个对象
        }
    </script>
</body>
</html>